The invention relates to an adjusting device for a disc brake and, in particular, an adjusting device for a pneumatically actuated disc brake. The adjusting device adjusts for wear of the brake pads and the brake disc of a pneumatically actuated disc brake having a rotary-lever-actuated brake application device, which adjusting device can preferably be inserted into an adjusting spindle of the disc brake and attached to a brake caliper of the disc brake by way of a bearing disc.
Adjusting devices or wear adjustors for disc brakes exist in various embodiments. DE 10 2004 037 771 A1 (having U.S. published counterpart application US2007/209890 A1) discloses an adjusting device for a disc brake, the specifications of which are expressly incorporated by reference herein. This adjusting device is suitable for a pneumatically actuated disc brake, in particular one of sliding-caliper design. Furthermore, the adjusting device can, however, also be used in pneumatically actuated fixed-caliper or pivoting-caliper disc brakes.
Pneumatically actuated disc brakes have over time become standard equipment on heavy commercial vehicles. Such disc brakes require mechanical boosting or “force amplification” in order to produce the demanded brake application force, because the force of the pneumatically charged brake cylinders is restricted on account of the pressure level (at present approximately 10 bar) and the limited structural size of the brake cylinder. Presently known pneumatically actuated disc brakes have boost ratios of between 10:1 and 20:1. The piston strokes of the brake cylinders are in the range from 50 mm to 75 mm, resulting in brake application travels of approximately 4 mm for pressing the brake pads against the brake disc.
The friction material thickness of the brake pads lies in the range of 20 mm, and because two pads are installed, this results in a wear travel of approximately 40 mm, not taking disc wear into consideration. This travel is a multiple greater than the abovementioned brake application travel. It is therefore necessary for the brake to be adjusted correspondingly to the pad wear by way of a device. The prior art provides automatic wear adjustment by way of which the so-called air play, that is to say the gap between the brake pads and the brake disc in the non-actuated state, is kept constant independently of the wear state and wear behavior of the brake pads.
In commercial vehicles, use is very often made of disc brakes which have an adjuster which is arranged concentrically in the cavity of a threaded spindle and which is driven eccentrically by a rotary brake lever via a drive element (for example switching finger or toothed wheel). During a braking process, the rotary lever which is coupled to the piston rod of the brake cylinder performs a rotational movement. Before the rotational movement of the lever is introduced into the adjuster via the coupling mechanism of the adjusting means (for example shift fork and shift finger or toothed wheel), a so-called idle travel must be overcome. This travel is decisive of the size of the so-called air play, because during the movement, the adjustment is not activated, and the brake application travel therefore constitutes the air play. After the idle travel is overcome, the adjuster is set in a rotational movement, and an adjusting process is initiated by the coupling to the threaded spindle or tube.
DE 10 2004 037 711 A1 describes an adjuster of the type, which is shown in FIG. 5. The adjuster is composed substantially of the following functional elements: shaft 2; bearing disc 3; axial bearing 5; collar bush, or spacer sleeve 19; shift fork, or drive ring 6; ball ramp clutch 7; cone clutch 17; and cylindrical spring 12. With regard to the description, reference is made to DE 10 2004 037 711 A1.
The adjusting device must basically perform two functions:
1. the automatic air play adjustment; and
2. the manual restoration or retraction of the adjusting mechanism upon replacing of the brake pads.
When being turned back, for example to replace the brake pads, the adjusting device is turned back or retracted by hand using a screwdriver from its so-called wear position into its initial position. Here, the adjusting device must be turned counter to the blocking direction of the freewheel. Since the freewheel however has a 100% blocking action, turning back cannot be carried out without special design measures.
It is therefore the object of the present invention to provide an adjusting device with improved manual restoration, with the above disadvantages being eliminated or significantly reduced, and further advantages being obtained.
This and other objects are achieved by an adjusting device for adjusting for wear of the brake pads and the brake disc of a pneumatically actuated disc brake having a rotary-lever-actuated brake application device, which adjusting device can preferably be inserted into an adjusting spindle of the disc brake and attached to a brake caliper of the disc brake by way of a bearing disc. An axial bearing is formed axially on one side of a drive ring and a ball ramp clutch with freewheel function is formed axially on the opposite side of the drive ring. The ball ramp clutch has balls, a drive bush arranged at the drive input side axially between the axial bearing and the balls thereof and a drive-output-side clutch ring. A cone clutch is arranged between the drive-output-side clutch ring and a spring sleeve for a cylindrical spring. The drive-output-side clutch ring is designed for a working angle of rotation as limited by at least one stationary stop.
The working angle of rotation is to be understood to mean the angle of rotation by which the adjusting device is rotated in the event of an automatic adjustment process during a braking process.
As a result, it is achieved that, during a turning-back operation, the blocking action of the freewheel is eliminated for this operating situation by virtue of the drive-output-side clutch ring being prevented from rotating, which is possible by way of a stationary stop. At the same time, a limited working angle of rotation is provided which permits the automatic adjustment in the opposite direction of rotation of the drive-output-side clutch ring.
This design offers the following advantages:
(1) relatively low force expenditure during a manual turning-back operation, because no load shift clutch need be overcome;
(2) no additional components required for the restoring mechanism; and
(3) cost-effective production by way of non-cutting shaping technology.
A directional clutch which acts in the axial direction is installed in this adjusting device. The directional clutch is formed from a ball ramp system and a friction clutch, in particular a ball-cone clutch.
When turning back by hand, the rotational movement is introduced via the shaft and the spring sleeve initially into the ball-cone clutch. From there, the movement is transmitted into the ball ramp clutch by way of the frictional engagement in the ball-cone clutch. Since the ball-cone clutch and ball ramp clutch are designed for self-locking, the clamping action takes effect. Turning back is therefore not directly possible. To permit turning back, it is necessary for the clamping action of the directional clutch to be eliminated.
If the drive-output-side clutch ring is prevented from rotating, the clamping action of the freewheel system can be suppressed. The bore of the clutch ring therefore has a profiling, by which the ring is prevented from turning back in the so-called rest position of the adjuster. The clutch ring is supported on a stop, preferably on a stop of the rotationally fixedly mounted collar bush, which has an external profiling matching the internal profiling of the clutch ring. The two profilings are coordinated with one another such that the clutch ring has the clearance necessary for the working angle of rotation for the automatic air play adjustment.
In order that the clamping action of the freewheel is not present in the rest position, it is highly important that the collar bush and the clutch disc which is coupled by way of the profiling are positioned correctly.
In a preferred embodiment, the stop is integrally formed on an end section of a collar bush which extends axially through the ball ramp clutch and through the drive-output-side clutch ring, the other end of which collar bush has a collar which forms a stationary section of the axial bearing. In this way, a component is provided which has multiple functions and which reduces the number of different parts and facilitates assembly.
It is also preferable for the other end of the collar bush, which end forms the stationary section of the axial bearing, to be fastened in a rotationally fixed manner to the bearing disc which is attached to the brake caliper.
The cone clutch is preferably a ball-cone clutch which has the drive-output-side clutch ring and a tapered bush which is connected to the spring sleeve. Clamping balls are arranged between the drive-output-side clutch ring and the tapered bush.
The axial bearing is formed by one side of the drive ring, by rolling bodies and by a collar of a collar bush which extends axially through the ball ramp clutch. This likewise reduces the number of different parts and provides a compact design.
A disc brake, in particular pneumatically actuated disc brake, has an adjusting device according to the above description.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.